1. Field of the Invention
The invention pertains to guides for roller valve lifters for internal combustion engines which prevent rotation of the valve lifter about its axis in order to maintain the lifter roller properly oriented to the associated cam lobe.
2. Description of the Related Art
Roller valve lifters for internal combustion engines use a roller at the lower end of the valve lifter for engaging a cam lobe. The use a roller with the valve lifter reduces friction, provides extended cam life, improves engine efficiency and vehicle mileage and improves lifter life. Because the lifter roller must rotate about an axis parallel to the axis of rotation of the camshaft operating the lifters, guide means must be used to properly maintain the orientation of the axis of the lifter roller to the axis of the camshaft.
To properly orient the roller of an engine valve lifter the outer end of the lifter is provided with parallel flat surfaces located upon opposite sides of the lifter axis. These flat surfaces are oriented to the axis of the valve roller and cooperate with guide structure mounted upon the engine to maintain the proper orientation of the valve lifter roller to the cam lobe during engine operation while the valve lifter reciprocates within its bore defined in the engine block.
Previously, guides for roller valve lifters of internal combustion engines are formed of stamped metal, or powdered metal, having an opening of a non-circular configuration including flats which corresponded to the configuration of the lifter flats. The lifter reciprocates within the guide openings with a controlled clearance, the dimension across the guide flats being less than the basic diameter of the cylindrical lifter. A retainer is employed to locate and mount the guide upon the engine.
Such conventional metal guides have several disadvantages. For instance, as the guide restrains the lifter against rotation restraint is a function of metal-to-metal interface contact, and wear will occur on the interfaces which increases the tolerances therebetween, and as wear occurs the ability of the guide to properly orient the valve lifter with respect to the cam lobe diminishes, resulting in excessive roller and cam wear.
Another deficiency of conventional metal valve lifter anti-rotation guides results from the fact that the metal guide is heavy and cumbersome, and hence are expensive to manufacture and produce. Further, metal valve lifter guides generate unwanted engine noise.
Yet another deficiency of conventional metal valve lifter guides is due to the multi-part nature of the assembly which results in time consuming assembly which is subject to errors which can lead to engine failure and significant damage.